Gases - Fundamentals of Industrial Chemistry: Pharmaceuticals, Polymers, and Business - page 24

from high fabrication costs, brittleness, and degradation due to oxidation.
Polymer-based membranes may the most economical to produce and easiest
to fabricate, but often suffer from limited selectivity and low flux. There
is continued research to modify the polymer structure to improve these
properties.
For the separation of carbon monoxide and hydrogen, often a combination
of techniques - cryogenics, PSA, and membranes - is used.

3.2 NITROGEN AND OXYGEN

Nitrogen and oxygen are prominent industrial gases and are obtained by
separation from air. Air is about 78% by volume nitrogen, 21% oxygen,
0.9% argon and smaller amounts of other gases. Nitrogen is a colorless,
odorless, tasteless gas with a specific gravity of 0.967 and a boiling point
off” 196 ∘ C. The specific gravity of a gas is the density of the gas divided by

the density of air. The density units cancel so specific gravity is unitless. The
specific gravity of a liquid is the density of the liquid divided by the density
of water.
Because nitrogen is ubiquitous, there is some familiarity with it, but it can
be dangerous and can cause death if someone is in a nitrogen atmosphere
with insufficient oxygen. I worked at one location when they held their 25th
anniversary of operation. The site manufactured several toxic gases: carbon
monoxide, phosgene, and chlorine, yet the two fatalities in the site's operating
history were not from these, but from nitrogen. In a tragic accident, a worker
went into an area that had been blanketed with nitrogen and a second worker
was also overcome when he went to rescue the first worker. More recently,
in 2011 at a Shintech vinyl chloride plant in Plaquemine, LA, two workers
died after entering a vessel that had a nitrogen atmosphere [13]. Nitrogen
is commonly used industrially to provide inert atmospheres and prevent fires,
but precautions must be taken before entering these atmospheres. There is also
the danger associated with any pressurized gas. In 2013, at a CF Industries
plant in Louisiana that manufactured ammonia, a manifold ruptured during
off-loading of nitrogen gas. One worker was killed and seven others were
injured [14].
Oxygen has a boiling point of

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183 ∘ C which is sufficiently different from
nitrogen that the two components can be separated from air by a cryogenic
distillation. Nitrogen has the lower boiling point and exits from the top of
the fractionating column and oxygen from the bottom. In laboratory usage
of liquid nitrogen, such as in a Dewar flask, care should be taken to avoid
condensation of oxygen which can accumulate if the Dewar is continually
“topped off” with more liquid nitrogen rather than allowed to evaporate to

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